The aide paused uncertainly, then bowed his head and handed back the reins. At once Napoleon wheeled the horse about to watch the cream of his army cross the floor of the valley, slowly disappearing into the dense cloud of powder smoke that had gathered as a result of the French batteries’ bombardment of the ridge throughout the day. Ney halted the formation and ordered them to form square, then the Guard continued their advance, five battalions to the front, and four behind, in reserve.

Soult had taken a horse and now rode up to the Emperor. He pointed towards the line of the ridge as it turned to the north-east of the battlefield. The dark shape of a distant column was approaching Wellington’s left flank, and clearly visible to the men of d’Erlon’s corps.

‘Sire, those are Prussians.’

‘Quiet, Soult!’ Napoleon snapped. Glancing round, he saw that none of the soldiers seemed to have overheard. He turned back to his chief of staff. ‘I know what they are. But you will ride down the line and tell our men that it is Grouchy, come to save us.’

‘Sire?’

‘Our fate hangs by a thread, Soult. Our men need to believe they can win, or we are finished. Now go, tell them!’

Soult nodded as he grasped the necessity of the lie. He took a deep breath and spurred his horse along the front ranks of d’Erlon’s corps. Snatching off his hat he waved it from side to side and then thrust it towards the distant column.

‘Men! See there! It is Marshal Grouchy! Grouchy is coming! Wellington is beaten!’

His words were seized on eagerly and the men cheered wildly, and then began their own advance to the right of La Haye Sainte. The roar of their voices carried across the valley to where the Imperial Guard continued their relentless approach to the ridge. Marshal Ney paused at the rear of the column. He glanced back towards Napoleon, waved his hand, and then turned to the front as he drew his sword and urged his horse forward, disappearing into the smoke.

The allied centre, 7.30 p.m.

‘Heads up!’ a soldier from Halkett’s brigade shouted. ‘Here they come again!’

Arthur had just led two battalions of Brunswick infantry forward to the ridge. The inexperienced young men looked ahead nervously as they heard the shout and guessed its import. Even though the French guns had continued to fire on the ridge, there had been no attacks for nearly an hour and Arthur had used the opportunity to pull in his flanks and concentrate what was left of his army astride the road to Brussels. Halting the Brunswickers, he rode ahead with Somerset and Uxbridge as far as the hedge on the crest and looked down the slope. The sound of drums drifted through the smoke.

‘Infantry again,’ said Uxbridge.